[9349] in linux-scsi channel archive
Re: shared SCSI buses
daemon@ATHENA.MIT.EDU (Kurt Garloff)
Fri Aug 11 06:14:29 2000
Date: Fri, 11 Aug 2000 12:10:27 +0200
From: Kurt Garloff <garloff@suse.de>
To: David Teigland <teigland@sistina.com>
Message-ID: <20000811121027.C16909@D250.suse.de>
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Hi,
On Thu, Aug 10, 2000 at 07:33:50PM -0500, David Teigland wrote:
> I'm interested in combining two or more active hosts with multiple device=
s on a
> single parallel SCSI bus. I've successfully done this, but don't know the
> extent of problems which could arise when hosts or disks are added or rem=
oved
> (crashed) on the in-use bus.
Yes, multi-initiator environments are well defined in SCSI.
> A) How likely is it that the scsi driver(s) will see errors when nodes a=
nd=20
> drives come and go and are there specific cases which are bad?
SCSI bus is electrically NOT designed for hot-swapping. If your bus is idle
at the time you connect or disconnect a device, nothing bad happens, but
this can not be guaranteed in case where you have data being transfered over
the bus.
But there are designs (SCA connector), where some care for the electrical
problems is taken.
> B) What are the possibilities of a node surviving if it sees scsi errors?
Error handling in Linux SCSI strongly depends on the situation and the
adapter driver being used. Possible reaction range from retrying a command
that failed or reporting EIO to the app to serious things such as bus
resets, which can cause problems to your SCSI subsystem.
> C) How much work would it take to make all these odd cases reliable?
General SCSI error handling improvements. Talk to Eric Youngdale about this
and discuss it here, please.
> I'm interested in the status on both 2.2 and 2.4.
Funnily, you did not mention the filesystem problems:
If you mount any partition read-write with one machine, you are not supposed
to mount it from any other machine. Not even ro, as the kernel does caching
and will see an inconsistent FS, which can cause problems.
Have a look at GlobalFilesystem, if you look for a solution for this proble=
m.
Sharing partitions ro works perfectly just out of the box.
Regards,
--=20
Kurt Garloff <garloff@suse.de> Eindhoven, NL
GPG key: See mail header, key servers Linux kernel development
SuSE GmbH, Nuernberg, FRG SCSI, Security
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